Carcinoid tumors are neuroendocrine tumors arising from enterochromaffin (EC) and related cells found in epithelial organs throughout the body. EC cells are the most common endocrine cells and are frequently identified in the mucosa of the intestine and bronchus. Carcinoid tumors synthesize and store a variety of vasoactive substances and hormones. The tumors are commonly classified based on their embryologic site of origin into carcinoids of the foregut, midgut, and hindgut. Tumors within each subgroup...